Piezoelectric materials have been widely used in various applications. Several attempts have been made to use them in the field of power generation, using ceramic piezoelectric materials with minimal success. Since the discovery of piezoelectricity in polymers in 1969, various application-based studies have been reported. Polymers are now well known candidates for piezoelectric material, having a charge displacement coefficient, d33, of approximately 35 pC/N. Polymers and polymer blends are easy to melt extrude into thin films or fibres. They have a relatively low melting temperature (for example, polyvinylidene fluoride (PVDF) melts at around 175° C.) thus making them easier to process than ceramics. The availability of flexible polymers exhibiting highly piezoelectric behaviour, coupled with our increasing need for renewable energy, now makes the generation of electrical energy using piezoelectric materials an attractive option.
Previous work on polymers as piezoelectric materials has reported developments in thin film or bulk samples. Polymer fibres may have various potential applications, such as sensors, actuators, and energy scavenging devices. When the fibres are used in the form of two-dimensional structures, such as in textiles, or one-dimensional structures, such as ropes, the potential for new energy scavenging application is vast. Possible energy scavenging textile applications may include structures for harvesting mechanical energy from wind, rain, tidal, and waves for electrical power generation.
Previous work has included a proof of concept for an energy harvesting technique that uses macro-fibre composite (MFC). The MFC used in this work was a composite of piezoelectric lead zirconate titanate (PZT) fibres. Since PZT fibres are not flexible, they need to be prepared as composites for use as energy scavenging piezoelectric materials. On the other hand, polymer fibres are flexible, and can be used in making composite materials and two- and three-dimensional composite structures. Hence, they may be used in wider applications, especially if they may be manufactured more cost effectively than piezoelectric ceramics.
Previous work has included a complex multi-stage process for preparation of a piezoelectric copolymer fibre in a multi-layer construct. However, the fabrication method is complex, and requires many processing stages which may not be easily combined into a streamlined continuous production process.
Therefore, an aim of embodiments of the present invention is to provide an improved piezoelectric polymer element, such as a fibre or film, having a simple structure. Another aim of embodiments of the present invention is to provide an improved method for producing such a piezoelectric polymer element via a continuous process. A further aim of embodiments of the present invention is to provide apparatus for producing a piezoelectric polymer element using such an improved method. Further aims of embodiments of the invention are to provide a piezoelectric construct comprising such an improved piezoelectric polymer element for converting mechanical energy into electrical energy, and to provide a power conversion system comprising such a piezoelectric construct.